Is Global Warming Behind Hurricane Katrina?

This is a partial transcript of "Special Report With Brit Hume," August 30, 2005, that has been edited for clarity.

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BRIT HUME, HOST: A writer in the "Boston Globe" today declared that the hurricane that has wreaked such damage along the Gulf Coast may be called Katrina, but it’s real name, he said, is global warming.

Journalist and author Ross Gelbspan noted that Katrina began as a minor hurricane but that was before, "It was supercharged with extraordinary intensity by the relatively blistering sea-surface temperatures on the Gulf of Mexico," which he says or suggests were a consequence of global warming.

Let’s ask Patrick Michaels, senior fellow in environmental studies at the libertarian CATO Institute and a professor at the University of Virginia, about all this. He joins me from Charlottesville, Virginia.

Dr. Michaels, welcome. Thank you for coming in and agreeing to talk to us about this.

What about this idea that we had a minor hurricane, drifted across Florida with little damage, and then got reheated by the very hot water in the Gulf of Mexico (search) into this catastrophic hurricane?

Secondly, Ross Gelbspan (search) put forth a very testable scientific hypothesis, didn’t he? He said that, as sea-surface temperature goes up, hurricanes will become more extreme.

Well, you can take a look at data for the Atlantic basin for the last 50 years, and you’ll find that only 10 percent of the variation in hurricane strength and frequency from year to year is related to sea-surface temperature.

In other words, 90 percent in the changes in hurricanes, weak years, strong years, not very many, years with a lot, 90 percent of that variation is due to factors other than sea-surface temperatures.

HUME: What kind of factors are we talking about here?

MICHAELS: Well, whether or not there’s an El Nino (search), for example. You know, that’s that big temperature reversal out in the Pacific that causes all kinds of news stories.

HUME: Does that have anything to do with global warming, by the way?

MICHAELS: Well, that’s a very interesting point. A lot of scientists, not necessarily me, think that El Nino frequency would go up if there was global warming. Well, El Nino is poison to hurricanes. It induces westerly winds over the Atlantic Ocean (search), and westerly winds kills hurricanes. That’s one of the reasons why sea-surface temperature is not this big, explanatory variable.

And you know what? There’s another way to test this pretty grossly. The world’s temperature, surface temperature, has gone up over the last few decades, not as much as a lot of computer models forecast, but it’s gone up.

So ask yourself the question, has the number of hurricanes, meaning tropical cyclones around the world, gone up? In other words, does global warming increase global hurricanes? And you will find that there has been no statistically significant change whatsoever in the number of global tropical cyclones.

HUME: Well, I think people living in this country, who have vivid memories of hurricanes such as Andrew and others, have the sense, at least, that we have had an increase in these killer hurricanes, that they seem more frequent, in recent years, particularly — this year, there seems to have been a lot of them — and they might be tempted to believe that, well, you know, something’s causing this. Why not global warming?

Now, you’ve suggested one reason why not, but what about it?

MICHAELS: Well, again, the problem is, when you do science, and you make hypotheses, you’ve got to test global temperatures against global hurricanes, not against Atlantic hurricanes.

Yes, Atlantic hurricane frequency has increased since the late 1990s. But the fact of the matter is, it was quite low for several decades, ending about 1995, 1998, or so. We were below the long-term mean for several decades.

We’ve now come up to run above the long-term mean. And when you add several years of below and several years of above, you know what you get, Brit? Average!

HUME: Right, I understand. So is that where we are, I mean, overall for the...

MICHAELS: Overall...

HUME: It’s fair to say that this increase in global temperatures has been building over the past five decades or so, correct?

MICHAELS: That’s right. And you don’t see a concomitant change in the trends in global tropical cyclones.

HUME: So then, where would one look, then, to try to figure out what’s the cause of this recent spate of Atlantic hurricanes?

MICHAELS: Well, there’s the temperature fluctuation in the Atlantic that is well-known, known as the North Atlantic — well-known to nerds like me, excuse me, Brit — called the North Atlantic Oscillation (search). That’s in a phase that seems to be promoting hurricanes.

But you know, these numbers — again, like only 10 percent of the variation in Atlantic hurricane strength and frequency is related to the sea-surface temperature. That tells you something. Even if you’re going to warm up the planet, and we are — and I wish we could say we could stop it, but we can’t...

HUME: Quickly.

MICHAELS: ... what’s going to happen is that the signal of increased hurricanes will take forever to emerge from those very noisy year-to-year fluctuations, if the sea-surface temperature only explains 10 percent. And by then, we might not even be burning fossil fuel.

HUME: Dr. Michaels, always good to have you. Thank you very much. .

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